Technical Field
The present invention relates to wavelength division multiplexing and, in particular, to lens arrays used in conjunction with micro-mirrors to realize a low optical loss structure with good misalignment tolerance.
Description of the Related Art
One option for increasing the aggregate data rate in an optical system is to use wavelength division multiplexing (WDM) to transmit multiple signal channels in a single waveguide core. This increases the channel density, allowing substantially more information to be sent using the same number of fiber cores.
Recent efforts have been focused on integrating polymer waveguides with opto-electronic chip arrays (VCSEL and photodiodes) to increase the bandwidth density of an optical transmission system. Low cost fabrication techniques for high volume are being developed.
However, there are challenges in implementing WDM with conventional fabrication methods. Typically, micro-mirrors using a total-internal reflection mechanism or a gold metal coating are used to couple the light from the VCSELs into the waveguide cores and from the waveguide cores to the photodiodes. However, these micro-mirrors have no wavelength selectivity in the relevant spectral range and cannot be used as filters with light signals having multiple wavelengths. Therefore new optical layouts are needed that are easily fabricated at low cost, have a low optical loss and are compatible with a high core density in polymer waveguides and with multiplexing schemes. This is of particular importance for receivers, where several light channels having different wavelengths in the same core need to be de-multiplexed efficiently. Fabrication errors and irregularities leading to optical misalignment can substantially increase loss and bit error ratio, which is detrimental in an optical link. Moreover, to reach a high bandwidth, photodiodes arrays with small active regions and a low capacitance are needed.